Inversion of teleseismic S particle motion for azimuthal anisotropy in the upper mantle: a feasibility study

Farra, Véronique; Vinnik, Lev; Romanowicz, Barbara; Kosarev, G. L.; Kind, R.

doi:10.1111/j.1365-246x.1991.tb03905.x

Cited by 86 publications

(37 citation statements)

References 18 publications

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“…Then, although Sd P is coupled with SV , the record can be deconvolved by either SV or S H. If the particular horizontal component of the recorded S is weak relative to the other component, its waveform can be disturbed by coupling with the other horizontal component, due to shear wave splitting in the upper mantle (Farra et al, 1991). The disturbance looks like the derivative of the stronger component.…”

Section: Detection Techniquementioning

confidence: 99%

Broadband converted phases from midmantle discontinuities

2014

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A technique for detecting intermediate-period (6-12 s) Sd P phases converted from S to P at a depth d in the source region is described. Previously, these phases were detected in short-period array recordings of deep events. The main idea of our technique is to deconvolve the vertical component of a single record by the S waveform, and to stack the deconvolved components of a number of records, with appropriate time-shift corrections accounting for the difference of epicentral distance. Using this technique, the phases converted from discontinuities at around 660 km, 860 km, 1070 km, and 1170 km depths beneath Sunda arc are detected at seismograph stations in central and eastern Asia. Our data on '1070 km' discontinuity are very consistent with those inferred from short-period recordings of the same events at the J-array in Japan (Niu and Kawakatsu, 1997), but favour a few different discontinuities in the midmantle, rather than one with a strongly variable depth. When compared with a tomographic model of the mantle for the same region, our data suggest that '1070 km' discontinuity may act as a barrier for the downgoing lithospheric slabs.

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Section: Detection Techniquementioning

confidence: 99%

Broadband converted phases from midmantle discontinuities

2014

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“…This assumption is also made by KOSAREV et al (1984), FARRA et al (1991) and VINNIK and MONTAGNER (1996 to analyze P-SH conversions from upper-mantle discontinuities. In our synthetics, the azimuthal patterns of converted phases that develop for horizontal axes of anisotropy are qualitatively similar to the ''near-horizontal'' cases in each model family.…”

Section: Special Case-horizontal Symmetry Axismentioning

confidence: 99%

P-SH Conversions in Layered Media with Hexagonally Symmetric Anisotropy: A CookBook

Levin

Park

1998

Pure and Applied Geophysics

161

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Reflectivity synthetic seismograms demonstrate that the type, layering and orientation of 1-D anisotropy influences strongly the coda of teleseismic P waves at periods T \ 1 sec, particularly P-SH converted waves. We assume the simplest form of anisotropy described by an elastic tensor with a symmetry axis ŵ of arbitrary orientation. The resulting phase velocities vary as cos 2x with respect to that axis. Using three families of simple crustal models, we compare the effects of an anisotropic surface layer with reverberations caused by both ''thick'' and ''thin'' layers of anisotropy at depth. If anisotropy in the surface layer is significant, the polarization of direct P can be distorted to generate a transverse component, followed by Ps and a prominent shear reverberation converted from direct P at the free surface. If the anisotropic layer is buried, the first, and often the most prominent, arrival on the transverse component is the P-to-SH conversion at its upper surface. If the anisotropic layer is sufficiently thin, P-to-SH conversions from its boundaries interfere to form a derivative pulse shape on the transverse component, which could be mistaken as the signature of shear-wave splitting. If ŵ is horizontal, compressional (P) and shear (S) anisotropy both produce similar waveform perturbations with four-lobed azimuthal patterns, suggesting that a weighted stack of P coda from different back-azimuths would improve signal-to-noise. For ŵ tilted between the horizontal and vertical, however, the effects of P-and S-anisotropy differ greatly. The influence of P-anisotropy on P-to-S conversion is greatest for a symmetry axis tilted at 45°to the vertical, where its azimuthal pattern has two lobes, rather than four. Combinations of P-and S-anisotropy typically lead to a composite azimuthal dependence in the P-coda reverberations.

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“…l), the data of seismic refraction profiling in Germany indicate the azimuth of fast velocity near 20" (Bamford 1977;Fuchs 1983). According to Farra et al (1991), the bottom of this layer is at 55 km. The bottom depth of the thermally defined lithosphere in the central part of Europe is less than 100 km (Cermak 1982), implying that the layer where anisotropy with the E-W direction can be frozen is less than 50 km thick.…”

Section: Shear Wave Splitting and Long-range Refraction Profiling Datamentioning

confidence: 99%

Global patterns of azimuthal anisotropy and deformations in the continental mantle

Vinnik

Makeyeva

Milev

et al. 1992

Geophysical Journal International

Self Cite

497

299

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We present a summary of measurements of azimuthal anisotropy in the continental mantle based on the SKS technique and performed mostly with the active participation of the authors. The directions of polarization of the fast quasi-shear wave and the time delays between the quasi-shear waves are obtained at nearly 70 locations in all continents, except Antarctica. These data are interpreted in terms of lattice-preferred orientation of olivine which is caused by deformations in the mantle. The depth interval responsible for anisotropy is unknown but the data suggest that it may reach at least 300 km. The fast directions in SKS do not show clear correlation with the fast directions of the teleseismic P at the same seismograph stations.In the regions of present-day convergence the fast direction of anisotropy usually aligns with the plate boundary. This correlation implies that the direction of shortening is the same in the crust and the upper mantle. In the regions of rifting, the inferred direction of mantle flow usually aligns with the direction of extension in the crust.Outside the regions of recent tectonic activity we, most likely, observe a combined effect of frozen anisotropy in the subcrustal lithosphere and of recently formed anisotropy in the asthenosphere. On a global scale, in these regions there is a positive correlation between the absolute plate velocity directions and the fast directions of anisotropy. The correlation is especially strong in central and eastern parts of North America. A clear absence of any evidence of large-scale azimuthal anisotropy in the data of long-range refraction profiling for the upper 100 km of the mantle of that region implies that the effect in SKS is generated mainly at greater depths, in the asthenosphere. Orientation of olivine at these depths reflects recent and present-day flow in the mantle rather than processes of a distant geologic past.

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Inversion of teleseismic S particle motion for azimuthal anisotropy in the upper mantle: a feasibility study

Cited by 86 publications

References 18 publications

Broadband converted phases from midmantle discontinuities

Broadband converted phases from midmantle discontinuities

P-SH Conversions in Layered Media with Hexagonally Symmetric Anisotropy: A CookBook

Global patterns of azimuthal anisotropy and deformations in the continental mantle

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